A stationary blade of a high-temperature gas turbine is cooled by using part of compressed air to keep the blade metal temperature below a temperature which the blade material allows. In order to cool the stationary blade, cooling techniques such as impingement cooling, film cooling, shower head cooling, and pin fin cooling are generally used singly or in combination according to the blade inlet gas temperature.
FIGS. 4 and 5 are a plan sectional view and a perspective view, respectively, showing one example of the present air-cooled stationary blade. In FIG. 4, inserts 53 are installed along the blade profile 51 in the cooled stationary blade. The insert 53 is provided with a cutout 52 at the leading edge portion of the stationary blade.
At the leading edge portion of the stationary blade, shower head cooling 54 is performed from the portion of the cutout 52 provided in the insert 53. The reason why the cutout 52 is provided in the insert 53 at the blade leading edge portion only is that the leading edge portion is a region having a high pressure and it is impossible to blow out air to this portion at a low pressure after impingement cooling, so that air is blown out directly without passing through the insert 53.
At the blade head dorsal portion, blade dorsal portion, and blade ventral portion, impingement cooling 55 and film cooling 56 are performed through the insert 53 as shown in FIG. 4. At the portion where film cooling 56 is performed, the blowout strength must be made proper because, if the cooling air blows out too strongly, the cooling air is mixed with a main gas flow, thereby decreasing the inherent effect of film cooling.
At the blade trailing edge portion, pin fin cooling 58 is performed through pin fin holes 57, and the air after cooling joins with the main gas flow. Thus, the cooled stationary blade of gas turbine is cooled by combining several cooling techniques.
As shown in a perspective view of a cooled stationary blade of FIG. 5, an outside shroud 59 and an inside shroud 60 each have a cooling air inlet hole 61, and a stationary blade 51 lies between the two shrouds 59 and 60. On the surface of the stationary blade 51, ranging from the blade leading edge to the blade trailing edge, holes for shower head cooling, film cooling, and pin fin cooling are formed. Also, the two shrouds 59 and 60 are formed with shroud cooling holes 62.
Nowadays, as the inlet temperature increases with the improvement in gas turbine efficiency, an inlet temperature on the order of 1500.degree. C. cannot be overcome by air cooling only because air has a low heat capacity and a large quantity of air is required for cooling. Therefore, steam begins to be used as a cooling medium because steam has a heat capacity higher than that of air and a relatively small quantity is required for cooling.
For this reason, the stationary blade is configured so that the portions which can be cooled sufficiently by air is air-cooled, and the portions which is difficult to cool by air is steam-cooled. In the case of steam cooling, however, because extraction steam of a steam turbine constituting a combined cycle is used, the leakage of steam into the gas turbine is required to be eliminated for the reason of steam-side cycle.
Therefore, it is required that a cooling medium passage through which steam flows be closed to the outside and have a steam supply port and a recovery port. As an example of the stationary blade of gas turbine in which two kinds of cooling media, air and steam, Japanese Patent Application No. 8-190717 "Stationary Blade of Gas Turbine" has been disclosed.
An object of the present invention is to provide a cooled stationary blade of a gas turbine constructed by a stationary blade, and an outside shroud and inside shroud which hold the stationary blade between them, wherein the portions which can be cooled sufficiently by air is air-cooled, and the portions which is difficult to cool by air is steam-cooled, by which high temperatures can be overcome.